Imaging of internal organs is commonly done using a fiber optic catheter. This catheter often includes a pull-back mechanism for viewing a longitudinal section of the internal organ and is often needed to rotate in order to obtain a cross-sectional image and thus provide a three dimensional image of a volume of the internal organ. For applications such as cardiology, interventional radiology and gastroenterology, the imaging system will include optical coherence tomography (OCT) or optical frequency domain imaging (OFDI). Alternatively, it is also possible to obtain images via spectrally encoded endoscopy (SEE), where the linear spatial information is encoded into a spectral line (dispersed line) and the image is formed by rotating the fiber optic probe along its axis.
For these probes, an image is acquired when an inner core is rotated with respect to a cylindrical tube (i.e., the protective sheath of a catheter). However, in these probes, the true angular velocity of the imaging probe is not known, which leads to an artifact referred to non-uniform rotational distortion (NURD). NURD occurs at the point where the imaging signal is directed towards the tissue and can lead to significant distortion of the image and a concomitant reduction in the geometric accuracy of the image.
Optical encoders have been integrated with an OCT probe in order to determine the rotational angle or velocity at the distal end of the probe. This rotational information is further used to detect and compensate for NURD, which can be done via an optical encoder, see, for example, U.S. Pat. No. 8,712,506 for the use of optical encoder to detect the position and the rotation speed. However, in order to process the signals, electrical signals are used to generate the optical sensing signals, and then detect the optical signals using a detector. The detected optical signals are thus translated back into electrical signals for further processing, which introduces additional noise and the devices used for this process add further cost to the system. It is also difficult to miniaturize such systems, which is important for many applications where size is important, such as minimally invasive surgery, needle biopsy, etc.
Thus, there is a need for a sensing mechanism that can produce electrical signals directly for post-processing. It is also desirable to have a sensing mechanism that can produce and detect electrical sensing signals as sophisticated but inexpensive electronics. As the energy in such a process is not transferred from one domain (e.g. optical domain) to a different domain (e.g. electrical domain), no additional actuators and sensors are needed, which poses to lower the total cost of the system as well as minimizing the dimension of the system.